DESCRIPTION (as provided by applicant): Vascular cell adhesive interactions are important in health and diseases ranging from thrombosis and atherosclerosis to the vasculitides and cancer. Adhesion molecules including integrins, and signaling molecules including focal adhesion kinase (FAK) and immune receptors, are key in all of these processes, and are important targets of drugs currently approved and under development. This Program integrates studies at the atomic and cellular level on cell adhesion and signaling in the vasculature, with the overall aim of accelerating both the acquisition of new knowledge and the development of drugs to treat disease. It ties together a group of investigators with a long history of collaboration and interaction in the Harvard Medical Longwood Area. The investigators have expertise in a wide range of structural biology techniques including crystallography, EM, and NMR, enabling a multidisciplinary approach to solving important biological problems. Furthermore, expertise includes the extracellular, membrane, and cytoplasmic environments. The interactions between investigators with expertise in different structural techniques and different cellular environments provide important synergies between the projects in understanding signaling in the outside-in and inside-out directions across the plasma membrane. Project 1 (Springer) examines the structure and mechanism of activation of aIphalB3, its complexes with small molecules and macromolecules including fibrinogen and Del-1, and the structural basis for immune thrombocytopenic purpura. Project 2 (Springer) focuses on the molecular basis for rolling and firm adhesion through interaction of alpha4B1 and alpha4B7 integrins with ligands MAdCAM-1 and VCAM-1, and complexes with candidate therapeutic antibodies and small molecules. Project 3 (Wang) defines the structural basis for binding of leukocyte integrin aM and aX I domains to ligands C3bi, ICAM-1, and Del-1. Project 5 (Chou) defines the membrane-embedded triad structures of two archetypal members of the immune receptor family, (DAP12)2(NKG2C)1 and sigma2(NKp46)1. Project 6 (Eck) examines signaling at focal adhesions and explores activation of the tyrosine kinase of FAK by phosphatidylinositol phosphates through use of structures, cell biology, and small molecules. Administrative (Springer) and Protein Expression (Lu) Cores enhance efficiency of the PPG. (End of Abstract)